1. Field of the Invention
The present invention relates to a polishing robot and a polishing method using the robot.
2. Brief Description of the Prior Art
The polishing robot of the type relevant to the present invention has been disclosed in Japanese Laid-open Patent Application KOKAI 60-108262 (1985). This is a two-arm articulated robot comprising a first arm swingable about an axis, a second arm swingable about a free end of said first arm, a microvibrating polishing tool suspended at a free end of said second arm, each of said first and second arms being driven by a servo-motor which is controlled for normal or reverse rotation within a predetermined angular range to reciprocate the corresponding arm within the necessary angular range, thereby positioning the polishing tool and causing the tool to polish the surface of a workpiece such as a metal mold.
However, in the conventional robot of this type, the small servo-motors used for driving the first and second arms require some amount of torque for moving the arms and, hence, call for the interposition of speed reducers. When the arms are designed to be lengthy, however, the backlash of such servo-motor causes rattlings of the arm end which are of the order of several millimeters at the maximum so that on playback, the accuracy of polishing is sacrificed.
Generally, the action of an industrial robot follows the sequence of teaching--memory--playback and the locus of action, speed of action, and acceleration/deceleration characteristic are important factors. For this reason, usually the continuous path (CP) control mode or the point-to-point (PTP) control mode is utilized. The former CP control mode includes a direct teaching system in which the operator actually manipulates the industrial robot to let it memorize the coordinates of points to be scanned for continuous positioning for playback. In this system, such other conditions as speed of action can also be taught. For example, relating to such a direct teaching system, it has been proposed to compute the required playback speed by providing a means of generating direction data indicating the direction of movement of the tool in addition to the means of generating data indicating the position of the tool, storing these data by sampling lock at predetermined intervals and selecting the speed of playback based on the amount of change in stored position data and the change in direction data (Japanese Patent Application KOKAI 60-124706 (1985).
However, while the direct teaching system is generally a convenient system which does not require a program and the like, the teaching by the operator is difficult when the area to be polished is large.